Messeinrichtung für Mikroseismikbeobachtungen in Tiefbohrungen

Summary

A deep well seismometer and its auxiliary systems were developed in the Sektion Geowissenschaften der Bergakademic Freiberg. By the aid of these instruments microseismic observations were performed for the first time in a north German deep well in 1968.

The seismometer is a vertical instrument with a characteristic frequency of 1.3 c/s and a pendulum mass of 10 kg. It is adapted to a galvanometer amplifier so that the ground particle velocity is measured. An electrodynamical calibration of sensitivity was developed. The laboratory tests indicated that the seismometer is capable of long time operation for temperatures up to ∼150°C and pressures up to ∼800kp/cm².

The microseismic measurements have been performed in the frequency ranges 0.1 c/s-1c/s and 1 c/s-10c/s in the following depths:2200 m, 1700 m, 1200 m, 700 m, 200 m and 50 m. Simultaneously with the deep well measurements the noise on the earth surface was recordd. A short description of the evaluation method is followed by a more detailed discussion of the amplitude spectra and correlation functions of the recordings.